This patent application is related to co-pending patent application entitled UPGRADEABLE TELESCOPE SYSTEM and to co-pending patent application entitled FULLY AUTOMATED TELESCOPE SYSTEM WITH DISTRIBUTED INTELLIGENCE, both filed on instant date herewith and commonly owned by the Assignee of this patent application, the entire contents of both of which are hereby expressly incorporated by reference.
The present invention relates generally to telescopes, such as those commonly used for observing/photographing celestial objects. The present invention relates more particularly to a telescope system having an intelligent motor controller for accurately controlling telescope position and for precisely controlling the speed at which the telescope moves to facilitate tracking of celestial objects therewith. The present invention further comprises an optical encoder using two photodetectors operating in quadrature to provide enhanced servo control for the telescope positioning motors, a calibration circuit for assuring reliable operation of the encoder with LED""s having varying brightness characteristics and/or varying sensitivities of photodetectors and a rotatable mount which provides electrical communication to an altitude drive motor located in a fork thereof while mitigating problems due to undesirable wrapping of a power/control cable about the mount as the mount rotates.
Telescopes for observing and/or photographing celestial objects such as planets, moons, stars, galaxies, asteroids, comets, nebulae, and the like are well known. Such telescopes range in size from small, readily portable ones to large fixed ones which are permanently located in observatories. The smaller telescopes are commonly used by students, hobbyists, and amateur astronomers. The larger telescopes are generally only used by researchers and professional astronomers.
Common types of telescopes include refractor telescopes, reflector telescopes, Schmidt-Cassegrain telescopes and Maksutov-Cassegrain telescopes. Refractor telescopes have a light collecting objective lens which focuses the collected light upon an eyepiece. The eyepiece, in cooperation with the objective lens, provides the desired magnification.
A reflector telescope utilizes a primary mirror to collect light and a secondary mirror to reflect the collected light through an opening in the telescope tube to an eyepiece. The eyepiece is mounted upon the tube, typically near the front of the tube, and is positioned orthogonal to the tube. The eyepiece cooperates with the primary mirror to provide the desired magnification.
Schmidt-Cassegrain telescopes are similar to reflector telescopes, except that the secondary mirror of a Schmidt-Cassegrain telescope reflects the collected light through an opening in the primary mirror instead of through an opening in the tube. In this manner, the eyepiece can be located directly behind the primary mirror, which is convenient for some types of viewing and photography. Additionally, light enters a Schmidt-Cassegrain telescope through a thin, two-sided aspheric lens, known as a correction plate. Further, the secondary mirror is convex, so as to increase the effective focal length of the primary mirror.
Maksutov-Cassegrain telescopes are similar to Schmidt-Cassegrain telescopes, except that in Maksutov-Cassegrain telescopes light enters the telescope through a meniscus lens and an oversized primary mirror is used to provide an unvignetted field of view.
In viewing celestial objects with any type of telescope, it is necessary to continually move the telescope, so as to maintain the telescope in desired alignment with the celestial object. This is necessary to compensate for the rotation of the earth with respect to the cosmos. Thus, such continual realignment of the telescope maintains the desired celestial object within the field of view of the telescope as the earth rotates about its axis.
Smaller, portable telescopes of the reflector, refractor, Schmidt-Cassegrain, Maksutov-Cassegrain or any other desired type are typically mounted upon a tripod to facilitate portability and use of the telescope upon uneven outdoor surfaces, such as upon the ground, upon paved surfaces, such as roads or parking lots, or upon any other desired surface.
Two different types of mount, altitude azimuth and equatorial, are commonly used to removably attach a telescope to a tripod. Altitude azimuth (alt-azimuth) mounts provide a comparatively rigid and steady mount for the telescope, but are more difficult to maintain in alignment with the desired celestial object when the telescope is being aimed manually. Altitude azimuth mounts have only two perpendicular axes of rotation, which make the altitude azimuth telescopes inherently more rigid and stable than equatorial telescopes. The altitude axis of rotation allows the telescope to pivot with respect to the mount about an horizontal axis and the azimuth axis of rotation allows the telescope to pivot about a vertical axis. In order to maintain alignment of a telescope having an altitude azimuth mount with respect to a desired celestial object, it is generally necessary to move the telescope about both the altitude and azimuth axes, since the position of celestial objects generally varies in both altitude and azimuth as the earth rotates.
Equatorial mounts facilitate easier maintenance of alignment of the telescope with a desired celestial object, since the telescope must only be moved about a single axis so as to maintain such alignment. In an equatorial mount, two orthogonal axes are configured such that one of the two axes can easily be aligned so as to be parallel to the axis of rotation of the earth. Once such alignment with the earth""s axis of rotation is accomplished, then it is merely necessary to move the telescope about the other axis, so as to maintain alignment of the telescope with a desired celestial object. Thus, with an equatorial mount only a single axis of the telescope needs to be moved in order to maintain such alignment.
However, in an equatorial mount it is necessary to provide two additional orthogonal axes of alignment (similar to those of an altitude azimuth mount) in order to facilitate alignment of one axis so as to be parallel to the earth""s axis of rotation. Thus, an equatorial mount actually comprises an altitude azimuth mount plus two additional axes and thus has a total of four different alignment axes. Because the equatorial mount comprises four different alignment axes, and because each axis inherently decreases the stability of the mount, it is difficult to manufacture an equatorial mount which is as stable as a comparable altitude azimuth mount (which has only two axes of alignment).
However, although such contemporary telescopes have proven generally useful for their intended purposes, they do possess deficiencies which detract from their overall effectiveness. For example, motorized telescopes frequently lack the precision required to reliably locate (under computer control) more faint celestial objects when higher magnifications are utilized. Thus, it is frequently necessary to make tedious manual adjustments in order to locate a desired celestial object and to position the desired celestial object within the center of the field of view of the telescope.
It is desirable to provide a motorized telescope system having sufficient accuracy to generally locate celestial objects of interest without requiring excessive manual adjustment of the telescope.
Further, many motorized telescopes are incapable of accurately tracking a celestial object (again, under computer control) as it moves across the sky due to the earth""s rotation. While motorized telescopes frequently do provide some tracking capability, it is often not sufficiently accurate to facility celestial photography. Frequently, such tracking is accomplished by merely stepping the telescope drive motors when the position of the telescope has been determined to be substantially out of alignment with the desired celestial object. This result in jerky, sporadic movement of the telescope, which is too erratic for high quality photography.
Although the prior art has attempted to overcome this problem by utilizing telescope drive motors which run continuously during tracking, such telescope systems still tend to provide generally unsatisfactory results. The speed of such motors must frequently be varied so as to maintain desired tracking. However, such variances in the speed of the motors inherently results in alignment errors since the celestial object being tracked is moving at a constant speed. Further, even maintaining a steady speed will not facilitate celestial photography, unless the speed maintained is sufficiently close to the desired tracking speed so as to maintain the position of the celestial object being photographed within approximately the same position within the field of view. Of course, the ability to maintain the desired positioning of the celestial object being photographed within the field of view of the telescope is most important when high magnification and/or long exposure times are necessary.
It is desirable to provide a motorized telescope system in which the telescope drive motors operate at a substantially steady and accurate speed during tracking, such that a celestial object being photographed maintains a desired position within the field of view of the telescope for an extended length of time.
Further, manual adjustment of a motorized telescope may be necessary when the drive motors thereof overshoot the position of the desired celestial object during the initial location process. Unless the drive motors slow down as the position of the telescope nears alignment with the desired celestial object, inertia may cause the telescope to travel slightly past the intended alignment position. This is more likely to happen at higher magnifications. Thus, as the optical capabilities of telescopes continue to improve, the ability of motor drive systems to accurately and reliably position a telescope becomes more critical.
It is desirable to provide a telescope drive system which mitigates overshoot when moving the telescope into alignment with a desired celestial object.
Further, a problem encountered in the manufacture the optical encoders which provide position feedback for motorized telescopes involves the selection of LED""s for the encoder assembly. Such LED""s must have a brightness which is within a desired range in order to function properly in the encoder assembly. If the brightness of an LED is insufficient, then the pulse is generated by the encoder will have insufficient width such that when the pulses from two photodetectors should overlap, they will not overlap and when the brightness of the LED is excessive, the pulses will have too great of a width, such that the pulses from two photodetectors will overlap when they should not overlap. Thus, incorrect brightness of an LED will inhibit proper quadrature operation of an encoder assembly.
It is desirable that the photodetector provide an output having a substantially square waveform, i.e., wherein the corners of the pulses are not appreciably rounded and the slopes of the raising and falling edges of the pulses are generally vertical. This is necessary so as to allow the output of the photodetector to be provided directly to a microcontroller. If the waveform of the pulse is substantially degraded, i.e., has substantially rounded edges and/or excessively sloped rising and falling edges, then the output of the photodetector must be conditioned, so as to provide a signal which is suitable for input to a microcontroller. Typically, the microcontroller will be used to count the pulses input thereto within a given length of time, so as to determine the rate at which the pulses are being generated. Pulses which are not sufficiently well defined will not be counted, and a false determination of the position and/or speed of the telescope drive motor will result. Such a false determination of the position and/or speed of the motor will adversely affect the ability of the drive motor system to position the telescope accurately.
When the output of an LED is too weak, then the output pulse of a photodetector formed therefrom will tend to be rounded. The peak amplitude of the pulse may not be reached until some time after the encoder has gated the light to the photodetector. This will cause the pulse to be too narrow and possible have reduced amplitude. The rising edge of the pulse will be poorly defined and the pulse will possibly be unrecognizable by the microcontroller.
When the output of an LED is too strong, then the output pulse will tend to be too broad and may even begin to overlap adjacent pulses, making them indistinguishable from one another, particularly at higher motor speeds. This occurs because light from the LED is reflected by surrounding structures and begins to reach the photodetector before the encoder is aligned so as to gate the light through and continues to reach the photodetector even after the encoder has ceased to gate the light through. In this instance, the microcontroller will not recognized individual pulses and will again provide an inaccurate count.
In an attempt to mitigate this problem, contemporary practice requires that LED""s be tested prior to assembly into an encoder assembly, such that only those LED""s having a brightness within the desired range are utilized. However, such testing is a time consuming and expensive process.
Further, photodetector sensitivities can vary substantially. Indeed, matched LED/photodetector pairs are commonly sold so as to account for variations and brightness of the LED, as well as variations and sensitivity of the photodetector.
It is desirable to provide for the use of LED""s having a broad range of intensities and for photodetectors having a broad range of sensitivities in encoder assemblies, without adversely affecting the accuracy or reliability of the encoder assembly.
A problem occasionally encountered in the use of motorized telescopes is the undesirable twisting or winding of control and/or power cables around the telescope as the telescope moves in azimuth, as when a celestial object is being tracked for observation or photography for an extended period of time. The altitude motor of a motorized telescope is mounted upon a rotating portion of the telescope mount, typically the fork. Thus, as the telescope rotates in azimuth, the electrical cable which provides electrical power and/or control signals to the altitude motor tends to wrap around the mount.
If the electrical cables become wrapped tightly around the mount, they may cause damage, The cables and/or their connectors may be broken as the mount continues to move and pull the electrical cables even tighter. Such wrapping of the electrical cables may even topple the telescope as they are pulled tight. Toppling of the telescope is very likely to result in substantial and costly damage thereto. It is even possible that the telescope or nearby people may be hurt.
In an attempt to mitigate the problems associated with such wrapping of the electrical cables around the mount, slip rings have been used to transfer power and/or control signals from the stationary portion of the telescope mount to the rotating portion thereof. However, such slip rings are prone to problems caused by wear and contamination. Both wear and contamination result in poor electrical contact of the slip rings, making them difficult to maintain and unreliable.
It is desirable to provide a mechanism for mitigating the problems associated with electrical cables wrapping around the mount of a telescope as the telescope rotates in azimuth.
The present invention addresses and alleviates the above mention deficiencies associated with the prior art. More particularly, the present invention comprises a telescope system of the type commonly used to observe/photograph celestial objects. Although the present invention is discussed herein as being used for observing/photographing celestial objects, those skilled in the art will appreciate that such telescopes are also commonly used to observe/photograph terrestrial objects. For example, telescopes are frequently used in nature photography to facilitate photography at a distance, so that wild animals are not disturbed. Thus, discussion herein of celestial observation/photography is by way of example only and not by way of limitation.
More particularly, the present invention comprises a telescope system comprising a telescope, a tripod supporting the telescope, a mount attaching the telescope to the tripod so as to facilitate rotation of the telescope about two generally orthogonal axes, and at least one controller/motor drive assembly for effecting desired rotation of the telescope about at least one of the two generally orthogonal axes. Preferably, the present invention comprises two controller/motor drive assemblies, wherein one of the two controller/motor drive assemblies effects desired rotation about each one of the two generally orthogonal axes.
Each controller/motor drive assembly comprises an electric motor coupled to move the telescope about one of the two generally orthogonal axes, a control circuit coupled to drive the motor, and an encoder coupled to provide feedback from the motor to the control circuit to facilitate enhanced position control of the telescope. The control circuit is configured to cooperate with the encoder to cause the motor to position the telescope as desired.
The motor preferably comprises a DC motor. As those skilled in the art will appreciate, DC motors are inexpensive and the speed and direction of DC motors can be controlled simply by varying the voltage and/or pulse width (as in pulse width modulation control) applied thereto.
The control circuit preferably comprises a microcontroller, preferably a PIC 16C54 or similar microcontroller. Those skilled in the art will appreciate that a general purpose microprocessor may alternatively be utilized. Further, dedicated circuitry, preferably very large scale integrated (VLSI) circuitry, may be utilized.
The encoder preferably comprises an optical encoder of the type having a spoked or toothed wheel which alternately blocks and transmits light. Alternatively, various other types of encoders, e.g., magnetic, electric, etc., may similarly be utilized.
According to the preferred embodiment of the present invention, the encoder wheel is attached directly to the motor shaft. However, as those skilled in the art will appreciate, the encoder wheel may alternatively be located elsewhere along a gear train which communicates rotary motion from the motor to the telescope. However, it will be appreciated that resolution is enhanced by positioning the encoder proximate the motor, which rotates faster than other portions of the gear train.
According to the preferred embodiment of the present invention, an LED directs light toward the encoder wheel and two photodetector receive light from the encoder so as to facilitate operation of the encoder in quadrature, as discussed in detail below.
The control circuit is preferably configured to control a speed at which the telescope moves, so as to facilitate accurate tracking of a celestial object being view/photographed. Further, the control circuit is preferably configured to reduce the speed at which the motor is moving the telescope as the telescope nears a desired position thereof, so as to mitigate overshoot of the telescope.
Optionally, the control circuit is configured to receive a signal representative of an angle by which the telescope is to be moved and is configured to cause the telescope to move by that angle. Optionally, the control circuit is further configured to store a present position of the telescope, receive a desired new position of the telescope, calculate a difference between the present position of the telescope and the desired new position of the telescope, and cause the telescope to move by approximately the calculated difference.
According to the preferred embodiment of the present invention, a plurality of sensors, preferably two photodetectors, receive light from the light source, e.g., LED, after the light passes through the encoder wheel. The encoder wheel alternately permits light to travel from the light source to the light sensors and prevents light from traveling from the light source to the light sensors. Since movement of the encoder wheel is proportional to the speed of the motor, the output of the light sensors is representative of the speed of the motor. The light sensors are coupled to provide a signal to the control circuit which is representative of the speed of the electric motor to facilitate servo control of the electric motor.
The two light sensors are preferably configured to operate in quadrature, so as to provide enhanced resolution of the rotational position of the encoder wheel. The two light sensors are positioned apart from one another approximately the distance of one half of a radially extending tooth or sprocket of the encoder wheel, such that they are capable of sensing an intermediate position of the encoder wheel which cannot be sensed when only one light sensor is utilized. More particularly, the use of two light sensors configured to operate in quadrature facilitates the sensing of the following four positions of the encoder wheel: both sensors blocked, the first sensor not blocked and the second sensor blocked, the first sensor blocked and the second sensor not blocked, and both sensors not blocked. Since the use of only a single light sensor facilitates the sensing of only two positions of the encoder wheel, i.e., blocked and not blocked, quadrature operation doubles the resolution of the encoder wheel, thus providing enhanced position control of the telescope. More importantly, the use of quadrature facilitates determination of the direction of rotation of the motor.
According to the preferred embodiment of the present invention, a calibration circuit is coupled to the control circuit and to the light source, to set a brightness of the light source to a desired level. The light sensor(s) are coupled to provide a signal to the control circuit which is representative of a brightness of the light source and the control circuit is configured to determine a brightness of the light source from the signal. The control circuit is configured to vary the brightness of the light source, so as to maintain the brightness of the light source within a desired range.
Varying the brightness of the light source to maintain the brightness within a desired range allows construction of an encoder assembly comprising untested LED""s and photodetectors. Thus, the brightness of the LED""s and the sensitivity of the photodetectors does not have to be verified prior to construction of the encoder assembly. Eliminating the need for such testing or pre-selection of the LED""s and photodetectors substantially reduces the cost of manufacturing the encoder assembly.
Further, the ability to vary the brightness of the LED""s mitigates problems due to variations in brightness throughout the life of the LED, due to aging and/or soiling thereof. As those skilled in the art will appreciate, LED""s tend to vary in brightness during the life thereof. Also, contamination or soiling of the LED may cause its brightness to diminish substantially, thus requiring undesirable and time consuming maintenance of the encoder assembly.
The calibration circuit preferably comprises a plurality of resistors which are configured to be selectively placed into series with the LED, so as to limit current through the LED in a manner which provides the desired brightness thereof. The control circuit senses the brightness of the LED and selects the resistor(s) necessary to provide the desired brightness. Preferably, the resistors are switchable so as to be placed in parallel with one another and in series with the LED.
According to the preferred embodiment of the present invention, a motorized mount attaches the telescope to the tripod and facilitates positioning of the telescope as desired. The motorized mount comprises a base fixedly attached to a tripod. A fork is pivotally attached to the base via a fork pivot to facilitate movement of the telescope in azimuth. The telescope is pivotally attached to the fork to facilitate movement of the telescope in altitude. An azimuth motor is attached to the base and coupled to rotate the fork. An altitude motor is attached to the fork and coupled to rotate the telescope. An electrical cable extends from the base to the altitude motor, preferably through the fork, for providing electrical communication to the altitude motor, preferably from either a controller/motor interface or from a hand-held motor control.
In order to mitigate problems associated with the electrical cable wrapping around the mount and/or the tripod, stops are provided to limit rotation of the telescope about the azimuth axis. More particularly, a base stop is formed upon the base, a fork stop is formed upon the fork, and an intermediate stop is configured to rotate independently with respect to the base and the fork. The fork stop abuts the intermediate stop and the intermediate stop abuts the base stop when the fork is rotated less than two revolutions with respect to the base. Limiting rotation of the fork to less than two revolutions with respect to the base limits wrapping of the cable around the fork pivot, the mount, and/or the tripod.
The fork stop preferably comprises a post formed upon the fork and extending downwardly therefrom. Similarly, the base stop preferably comprises a post formed to the base and extending upwardly therefrom. The fork stop and the base stop are configured such that the do not interfere with one another as the fork rotates relative to the base.
Preferably, the intermediated stop is configured to rotate about the fork pivot. The intermediate stop is preferably defined by a lever which extends from the fork pivot and is rotatably attached thereto.
Thus, the present invention comprises a telescope system having an intelligent motor controller for accurately controlling telescope position and for precisely controlling the speed at which the telescope moves to facilitate tracking of celestial objects therewith. The present invention further comprises an optical encoder using two LED""s to provide enhanced servo control the telescope positioning motors thereof, a calibration circuit for assuring reliable operation of the encoder with LED""s having varying brightness characteristic and a brushless mount for providing electrical communication to an altitude drive motor located in a fork thereof.